Management of thermal fluctuations in lean NOx adsorber aftertreatment systems

ABSTRACT

A method and apparatus manage heat in exhaust gas in an aftertreatment system that employs a lean NOx adsorber. A de-sulfation hot line and cooling line are employed to control exhaust gas temperatures for adsorption, regeneration and de-sulfation cycles of the aftertreatment system where each cycle can require different chemical and exhaust gas temperatures independent of the engine operation. The method and apparatus include a SOx adsorber to provide greater system durability.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of International Application No.PCT/CA2004/000390, having an international filing date of Mar. 11, 2004,entitled “Management of Thermal Fluctuations in Lean NO_(x) AdsorberAftertreatment Systems”. International Application No. PCT/CA2004/000390claimed priority benefits, in turn, from Canadian Patent Application No.2,422,164 filed Mar. 14, 2003 and from Canadian Patent Application No.2,453,689 filed Dec. 17, 2003. International Application No.PCT/CA2004/000390 is hereby incorporated by reference herein in itsentirety.

FIELD OF THE INVENTION

This invention relates to methods and apparatuses for managing exhaustgas heat over the range of operating conditions required by a lean NOxadsorber aftertreatment system.

BACKGROUND OF THE INVENTION

Emissions controls for internal combustion engines are becomingincreasingly important in transportation and energy applications. Oxidesof nitrogen (NOx) are of particular concern. NOx forms during combustionin internal combustion engines.

A lean NOx adsorber (LNA) can be employed to remove NOx from exhaustgas. LNAs reduce NOx by trapping the NOx in a catalyst washcoat. NOxtrapping in the LNA is referred to herein as adsorption. The NOx storedin the washcoat is reduced to nitrogen gas (N₂) periodically. Thisreduction process is referred to as regeneration or a regenerationcycle.

Where sulfur is found in the engine fuel or where sulfur-containingengine lubricating oil has leaked into the combustion chamber, oxides ofsulfur can also be trapped within the LNA washcoat. As discussed in, byway of example, U.S. Pat. No. 6,393,834, sulfur poisoning of LNAs fromoxides of sulfur in the exhaust gas can interfere with the ability ofthe LNA to remove NOx. Removing these oxides of sulfur periodicallyduring operation of the engine helps to maintain the efficiency of theLNA. Processes employed to remove sulfur compounds are referred to asde-sulfation. Regeneration and de-sulfation cycles both require a lowoxygen potential (or “rich”) environment to be effective. Regeneration,de-sulfation and removal of NOx each work best when the exhaust gastemperature is within a different range.

The acid-based chemistry of the washcoat dictates the temperature rangesat which the LNA washcoat effectively traps NOx and SOx. In general,trapped sulfate compounds are more stable than trapped nitratecompounds. That is, the ability of the LNA washcoat to store sulfatesextends to higher temperature ranges than is the case for NOx. Forsimilar reasons, the temperature at which de-sulfation proceeds tends tobe higher than the temperature required for regeneration.

“De-sulfation temperature” is used herein to refer to that relativelyhigh temperature at which sulfur is effectively released from the LNAwashcoat. The performance of current LNA washcoats tends to deteriorate,mainly due to sintering, when exposed to temperatures in excess of 700°C. Exceeding 700° C. by a significant margin increases the rate ofdeterioration. De-sulfation temperatures can approach and exceed 700° C.leading to poor long-term performance of the LNA.

For regeneration of the LNA, a regeneration temperature which is lessthan the de-sulfation temperature is generally preferred.

During the adsorption phase, the exhaust gas is lean and NOx is beingtrapped within the LNA. Lower exhaust gas temperatures can be toleratedduring the adsorption phase and are selected to allow the LNA to adsorbNOx over a suitable range of the engine map. Preferred exhaust gastemperatures during an adsorption cycle can overlap with regenerationtemperatures and are generally lower than de-sulfation temperatures (allof which can depend on the washcoat composition, the reductant chosenand other factors within the aftertreatment system).

In light of the range of preferred exhaust gas temperatures that dependon the aftertreatment control sought for the LNA, flexibility inproviding those temperatures over the range of potential engineoperating conditions is important. Control over the temperature to whichthe LNA is exposed can both extend the life of the LNA and improve itseffectiveness at removing NOx from internal combustion engine exhaustgas. Moreover, the faster the regeneration or de-sulfation temperaturesare reached within the exhaust gas and then returned to preferredadsorption cycle temperatures, the less the fuel penalty forregeneration or de-sulfation and the less NOx delivered from the engineas a result of these cycles.

Oxidation of a reductant in the exhaust gas, referred to here as in-lineoxidation, can provide the heat and reductants to either regenerate orde-sulfate an LNA as well as create the reduced oxygen potentialenvironment for de-sulfation. Oxidation can be promoted by a catalyst.The catalyst should be located in close enough proximity to the enginethat exhaust gas temperatures are sufficient to cause the catalyst to“light-off” at engine out temperatures yet still be proximate enough tothe LNA to provide rich exhaust gas regeneration temperatures orde-sulfation temperatures. However, the LNA reactive capacity (theability of the LNA to trap NOx) is relatively low at the temperatureneeded for the effective operation of the reformer/oxidation catalyst.Therefore, consideration should be given to ensure that exhaust gaspassing through the LNA during an adsorption cycle is cool enough (forexample, placed distant from the engine) to allow the LNA to operateefficiently over a wide range of engine operating conditions.

All references to “upstream” and “downstream” herein describe therelative position of components of the aftertreatment in relation to thedirection of the flow of exhaust gas during an adsorption cycle of theLNA aftertreatment system (which may not be the same as the flow duringa regeneration cycle or de-sulfation cycle), unless otherwise stated.

The present technique provides methods and apparatuses for managingexhaust gas temperature using an LNA over a wide range of engineoperating conditions.

SUMMARY OF THE INVENTION

This present technique manages exhaust gas heat into an LNA duringadsorption, de-sulfation and regeneration cycles of the LNA. One aspectof the present technique provides a hot route that shortcuts or providesa bypass route around, a cooling path between the LNA and an oxidationcatalyst. Another aspect of the present technique provides a long routeor cooling route through the aftertreatment system. The coding routeallows the exhaust gas to cool where needed. Another aspect provides acooling route with a heat exchanger between an oxidation catalyst and anLNA for cooling the exhaust gas as needed. Another aspect of the presenttechnique provides a cooling route with a turbine between an oxidationcatalyst and a LNA for cooling the exhaust and extracting energy fromthe exhaust gas heat. This energy can be employed, in another aspect ofthe present technique, to introduce air into the exhaust gas stream tocool the exhaust (by dilution) when needed. Another aspect of thepresent technique provides for a sulfur trap to manage sulfur in theaftertreatment system.

An aftertreatment system treats NOx found in exhaust gas produced duringcombustion of a fuel within a combustion chamber of an operatinginternal combustion engine. The system comprises:

-   -   an exhaust line for directing the exhaust gas from the engine;    -   a lean NOx adsorber disposed in the exhaust line;    -   a first catalyst disposed in the exhaust line upstream of the        LNA, the catalyst capable of oxidizing a reductant in the        exhaust gas;    -   a reductant line for delivering a reductant from a reductant        store to the catalyst;    -   a reductant flow control disposed in the reductant line for        controlling flow of the reductant into the exhaust line; and    -   a flow control for controlling flow of exhaust gas through the        hot line and the cooling line.        The exhaust line is capable of delivering exhaust gas from the        first catalyst to the lean NOx adsorber.

In one embodiment of the aftertreatment system, the cooling line and thehot line are placed between the catalyst and the NOx adsorber. Thecooling line is preferably longer than the exhaust line.

The system can further comprise a turbine, disposed within the coolingline, which drives an air blower disposed in an air dilution line forcompressing and directing air into the cooling line.

In one embodiment of the system, an air blower disposed in an airdilution line can compress and direct air into the cooling line. A heatexchanger can also be disposed in the cooling line.

The aftertreatment system can further comprise a close-coupled catalystin the exhaust line upstream of the system's first catalyst. Thereductant line delivers reductant to the exhaust line, upstream of theclose-coupled catalyst. In another embodiment, the reductant linedelivers reductant upstream of the first catalyst.

In a further embodiment of the system, the exhaust line can comprise abypass line employed to direct exhaust gas around the first catalyst.

The aftertreatment system can further comprise a SOx adsorber, disposedin the exhaust line relative to the NOx adsorber, to remove SOx from theexhaust gas before it passes through the NOx adsorber. In a preferredembodiment, the exhaust line further comprises a sulfur line forbypassing exhaust gas around the NOx adsorber when regenerating the SOxadsorber, and a flow control for controlling exhaust gas flow throughthe sulfur line.

An aftertreatment system is disclosed, for treating NOx found in exhaustgas produced during combustion of a fuel within a combustion chamber ofan operating internal combustion engine. The system comprises:

-   -   an exhaust line for directing the exhaust gas from the engine        and through the aftertreatment system;    -   a lean NOx adsorber disposed in the exhaust line;    -   a first catalyst disposed in the exhaust line, the catalyst        capable of oxidizing a reductant in the exhaust gas;    -   a reductant line for delivering the reductant from a reductant        store to the exhaust line upstream of the catalyst;    -   a reductant flow control disposed in the reductant line for        controlling flow of the reductant into the exhaust line;    -   a SOx adsorber disposed in the exhaust line;    -   a sulfur line capable of bypassing exhaust gas around the NOx        adsorber;    -   a flow control for controlling flow of exhaust gas through the        sulfur line wherein the exhaust line delivers exhaust gas from        the catalyst and the SOx adsorber to the lean NOx adsorber.

In a preferred embodiment, the system further comprises a sulfur linefor bypassing exhaust gas around the NOx adsorber, and a flow controlfor controlling exhaust gas flow through the sulfur line.

A method is also provided of operating an internal combustion engineequipped with an aftertreatment system for removing NOx from exhaustgas. The method comprises an adsorption cycle, a regeneration cycle anda de-sulfation cycle.

During the adsorption cycle the exhaust gas is cooled to within apredetermined adsorption temperature range when the exhaust gas is abovethe adsorption temperature range. The cooled exhaust gas is directedthrough an exhaust line to a lean NOx adsorber disposed in the exhaustline.

During the regeneration cycle, the exhaust gas is oxidized to a lambdavalue of less than or equal to 1, the exhaust gas is heated to within apredetermined regeneration temperature range when the exhaust gas isbelow the regeneration temperature range, and the oxidized and heatedexhaust gas is directed through the lean NOx adsorber.

During the de-sulfation cycle, the exhaust gas is oxidized to a lambdavalue of less than or equal to 1, the exhaust gas is heated to within apredetermined de-sulfation temperature range when the exhaust gas isbelow the de-sulfation temperature range; and the oxidized and heatedexhaust gas is directed through the lean NOx adsorber.

In preferred embodiments of the method, cooling the exhaust gas duringthe adsorption cycle, can further comprise one or more of introducingair into the exhaust gas, expanding the exhaust gas, and directingexhaust gas through a heat exchanger or through a turbine. In apreferred example, the turbine is employed to drive a blower fordirecting air into the exhaust line upstream of the NOx adsorber.

In additional preferred embodiments, cooling the exhaust gas can furthercomprise routing the exhaust through a cooling line, or directing aportion of the exhaust gas through the lean NOx adsorber or directingthe exhaust gas through a SOx adsorber disposed in the exhaust lineprior to directing the exhaust gas through the NOx adsorber.

In another embodiment of the method, exhaust gas is heated and oxidizedby passing the exhaust gas through a catalyst with a reductantintroduced into the exhaust gas.

The method can be practiced such that the reductant comprises one ormore of hydrocarbons, hydrogen, and/or combinations thereof. Inpreferred embodiments, the hydrocarbon comprises one or more of naturalgas, diesel, methane, ethane, butane, propane, and/or combinationsthereof.

Further aspects of the present technique and features of specificembodiments of the present technique are described below.

BRIEF DESCRIPTION OF THE DRAWINGS

In drawings which illustrate non-limiting embodiments of the presenttechnique:

FIG. 1 is a graph demonstrating flow of exhaust gas and temperature overthe range of engine operating conditions with adsorption (normal cycle),regeneration and de-sulfation zones.

FIG. 2 is a schematic diagram of a first embodiment of the presentaftertreatment system.

FIG. 3 is a schematic diagram of a second embodiment of the presentaftertreatment system.

FIG. 4 is a schematic diagram of a generalized embodiment of the presentaftertreatment system.

FIG. 5 is a schematic diagram of a third embodiment of the presentaftertreatment system.

FIG. 6 is a schematic diagram of a fourth embodiment of the presentaftertreatment system.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT(S)

A method of and apparatus for managing exhaust gas heat in a LNAaftertreatment system, are disclosed. The LNA is employed to treatexhaust gases created during combustion of a fuel in an engine'scombustion chamber. Relatively low exhaust gas temperatures (less than450° C. by way of example) are typically needed for effective operationof the LNA. However, high temperatures and a reducing atmosphere arealso needed periodically. These requirements are independent of enginespeed and load conditions. Thus, a means to independently control thetemperature at the LNA is desirable for effective system operation.

When needed, the exhaust gas is cooled from the engine by passing theexhaust gas through a cooling line which could embody a heat exchanger,a long route (long as compared to an exhaust gas route provided forwhere hot exhaust gas is desired), or a turbine driven blower, by way ofexample. When a reduced oxygen potential environment is desired, areductant, which can comprise, for example, methane, other hydrocarbonsor hydrogen, can be introduced into the exhaust line and oxidized. Thisreduces the exhaust gas and elevates the temperature of the exhaust gas.

FIG. 1 provides a graph of the flow of exhaust gas plotted againsttemperature. The area within curve 800 defines an example range offlow/temperature properties for exhaust gas exiting an engine block overoperating conditions of the engine. The area within curve 802 defines arange of target properties for the exhaust gas directed into a catalystduring regeneration. The area within curve 804 defines a range of targetproperties for the exhaust gas passing through an LNA during anadsorption cycle (normal cycle). The area within curve 806 defines arange of target properties for the exhaust gas through an LNA duringde-sulfation.

Care should be taken to ensure that temperatures are not so high as toexcessively reduce the durability or effective life of the LNA.Therefore, while curve 806 allows for effective de-sulfation, it may notbe desirable to allow exhaust gases within the LNA to be at the highesttemperatures within the range, depending on the properties of the LNA.Point A is a typical midpoint operating condition for the engine.

FIG. 2 is a schematic diagram showing an aftertreatment system accordingto one embodiment of the present technique. Exhaust lines flow from theengine and through the aftertreatment system and are made up of a numberof branches or alternate lines for controlling aftertreatment of theexhaust gases. These include lead line 12, line 12 a, hot line 49 andbypass line 20. Lead line 12 carries exhaust gases flowing in thedirection of arrow 14 from engine block 10 to a NOx aftertreatmentsystem where it can be directed through alternate lines that generallymake up an exhaust line. In the aftertreatment system, lead line 12carries exhaust gases to LNA 16, as indicated by arrow 14. Lead line 12branches to line 12 a and hot line 49 which bounds line 12 a.

Gases exiting LNA 16 are delivered to an outlet through lead line 12.Catalyst 18 is disposed in lead line 12 upstream of LNA 16.

The term “exhaust line” is used herein to include lines that carryexhaust gas within the aftertreatment system and into and out of theaftertreatment system.

Lead line 12 also branches to bypass line 20, which is capable ofcarrying a portion of the exhaust gases around LNA 16, as may bedesirable while LNA 16 is being regenerated or de-sulfated. The exhaustgas can be directed through bypass line 20 as indicated by arrow 22 byopening bypass valve 24. Bypass valve 24 can be disposed anywhere alongbypass line 20.

Valves 24 and 30 are provided to help control the flow of exhaust gasthrough lead line 12 during regeneration and de-sulfation.

Optional close-coupled catalyst 32 is provided in lead line 12physically proximate to engine block 10. A reductant, preferably methaneor another hydrocarbon or hydrogen, can be introduced just prior tocatalyst 18 and/or catalyst 32. Reductant valves 34 and 36 are disposedin respective main line 38 and close-coupled line 40, each of whichconnect back to store 44 from which reductant is supplied.

Hot line 49 bypasses line 12 a of the exhaust line running betweencatalyst 18 and LNA 16. Valves 51 and 57 are disposed in hot line 49 andline 12 a, respectively. Arrow 53 indicates flow direction in hot line49.

Temperature sensor 58 is employed to measure temperatures beforecatalyst 18 and LNA 16 as shown by the respective intersection points ofsensor feed lines 60 and 62 within lead line 12. Data flow is indicatedby data direction lines 63. Sensor 58 feeds temperature information tocontroller 64 through feed line 66 as indicated by data direction line67. Feed line 70 provides engine data to controller 64 as indicated bydata direction line 71. Controller 64 operates valves 24, 30, 34, 36, 51and 57 through feed line 72 as indicated by data direction lines 75.

FIG. 3 shows an aftertreatment system according to a second embodimentof the present technique. As in the embodiment shown in FIG. 2, exhaustgas is directed, as indicated by arrow 14, to LNA 16 from engine block10 through exhaust lines that include lead line 12 and hot line 86. Areductant can be introduced into lead line 12 through line 38 ascontrolled by valve 36 from store 44. Catalyst 18 is availabledownstream of the junction of line 38 and lead line 12 to allow for theexhaust gas to be heated and oxidized across catalyst 18 as needed.Exhaust gas temperature is further controlled by turbine-driven blower82 disposed in lead line 12. Blower 82 accepts exhaust gas, expands andcools the gas to extract energy from the gas, and uses that energy todirect air through line 84 and valve 80 as indicated by arrow 94 (in theembodiment shown) to lead line 12 downstream of turbine-driven blower 82and upstream of LNA 16.

The exhaust line includes hot line 86. Flow through hot line 86 iscontrolled by valve 90. Flow through line 91 is controlled by valve 88,as indicated by arrow 92.

FIG. 4 shows a generalized schematic diagram of an aftertreatment systemaccording to the present technique. FIG. 4 illustrates three possiblecooling loops to be attached between catalyst 18 and LNA 16 downstreamof hot line 142. Flow through hot line 142 is controlled by valve 140.Exhaust lines in this embodiment include lead line 12, hot line 142 andcooling lines 144, 146 and 148. Cooling lines, 144, 146 and 148, includecomponents of the exhaust line within the aftertreatment system. Heatexchanger route 144 has a heat exchanger disposed in lead line 12.Turbine route 146 has turbine 152 for converting heat energy of theexhaust gas (to a turbocharger by way of example). Long route 148 has anextended lead line 12 extended to allow for cooling of exhaust gas priorto delivering the exhaust gas to catalyst 16. Long route 148 and turbineroute 146 are versions of the embodiments provided in FIGS. 2 and 3respectively. One or more of the cooling lines, 144, 146 and 148, orother embodiments disclosed herein, could be incorporated into a LNAaftertreatment system.

Exhaust gas is generated by combustion events within one or morecombustion chambers disposed upstream of lead line 12 in engine block10. Exhaust gas results from the combustion of fuel. For example, thefuel could be hydrogen, a hydrocarbon such as natural gas, diesel orgasoline, or a mixed fuel that includes such fuels as natural gas ormethane or other hydrocarbons. Combustion of a fuel that combineshydrogen and a hydrocarbon fuel such as natural gas, diesel or a mixedhydrocarbon is also contemplated. The fuel is, in general, eitherdirectly injected into the combustion chamber or pre-mixed with aquantity of air to create a fumigated charge. In each case, sparkignition, hot surface ignition or compression ignition is utilized toinitiate the combustion process within the combustion chamber.

During an adsorption cycle of the aftertreatment system, it is desirableto maintain flow and exhaust gas temperature, within the area bounded bycurve 804 to help ensure adequate removal of NOx from exhaust gas withinthe lean, oxygen rich, exhaust gas environment. Considering the range ofoperating temperatures and flow rates for exhaust gas generated duringan adsorption cycle, an adsorption cycle of the aftertreatment systemrequires cooling of the exhaust gas from the engine prior to the LNAover at least a portion of operating conditions. This can beaccomplished by causing at least a significant portion of the exhaustgas to flow through a cooling line upstream from LNA 16.

During an adsorption cycle, LNA 16, under relatively cool, lean (oxygenrich) operating conditions, that is with an excess of oxygen availablein the exhaust gas, will drive NOx to (NO₃)₂ by way of: $\begin{matrix}\left. {{NO} + {\frac{1}{2}O_{2}\quad({Pt})}}\rightarrow{NO}_{2} \right. & (1) \\\left. {{XO} + {2{NO}_{2}} + {\frac{1}{2}O_{2}}}\rightarrow{X\left( {NO}_{3} \right)}_{2} \right. & (2)\end{matrix}$where X is in a washcoat (this is described further below).

Considering the embodiment of FIG. 2 again, valves 24 and 51 are closedand exhaust gas flows along lead line 12, including line 12 a. Theexhaust gases cool down in traveling along the extended route providedby line 12 a. That is, a cooling period through line 12 may be requiredto ensure that the exhaust temperature falls into area 804. The exhaustgas, at its desired temperature, passes through LNA 16 which removesNOx.

The extended route between block 10 and LNA 16 helps to provide for arelatively cool exhaust gas during adsorption. The route length providedby line 12 a and exhaust line material(s) employed upstream from LNA 16are selected to allow the exhaust temperature to fall within area 804across the range of operating loads. Alternatively, if the engine rarelyoperates within the highest temperature portions of area 800, theresulting NOx slip can be acceptable for a reduced length or moreflexibility in choice of materials for line 12 a.

In the embodiment of FIG. 3, the cooling loop, rather than an extendedline from catalyst 18 to LNA 16, includes turbine-driven blower 82disposed in lead line 12. Heat employed to drive turbine-driven blower82 and cool exhaust gas prior to LNA 16 is employed to drive acompressor drawing in air through line 84, past valve 80 and into leadline 12. The exhaust gas is diluted and cooled with cooler intake air.Valves, 90, 88 and 80 can be employed to adjust the temperature of theexhaust gases being delivered into LNA 16. Valve 88 is optional. Theturbine in turbine driven blower 82 can also be employed to drive ashaft if desired to generate work for other purposes.

FIG. 4 shows an embodiment having a generalized cooling loop. Here theexhaust gas route between catalyst 18 and LNA 16 is shown in coolingloops 144, 146 and 148. Specifically, a turbine is shown in cooling loop146. While employed for providing air dilution in the embodimentdiscussed for FIG. 3, it could be employed to extract energy from theexhaust gas heat to drive a generator or other such applications.

Also, air dilution from an independent air compressor could be directedin to the exhaust line. This compressor could be driven by a independentelectric motor or other independent energy source. Here, the turbinecould be eliminated.

The engine coolant or other coolant (such as air) could be incorporatedin a heat exchanger 150 to draw heat away from the exhaust gas whenneeded, as demonstrated in cooling loop 144. Cooling loop 148 is anextension of lead line 12. These methods can be employed to drive downexhaust gas temperature to provide for an adsorption cycle of thesubject aftertreatment system.

Eventually LNA 16 becomes less effective at removing NOx as X(NO₃)₂ usesup adsorbing sites in LNA 16. As such, periodic regeneration is requiredto remove NOx. Controller 64 determines when LNA 16 needs regenerating.

During regeneration, the following provides a set of reactions foundacross catalyst 18 where methane is the reductant: $\begin{matrix}\left. {{CH}_{4} + {2O_{2}}}\rightarrow{{CO}_{2} + {2H_{2}O}} \right. & (3) \\\left. {{CH}_{4} + {\frac{1}{2}O_{2}}}\rightarrow{{CO} + {2H_{2}}} \right. & (4) \\\left. {{CH}_{4} + {H_{2}O}}\rightarrow{{CO} + {3H_{2}}} \right. & (5) \\\left. {{CO} + {H_{2}O}}\leftrightarrow{{CO}_{2} + H_{2}} \right. & (6)\end{matrix}$where reaction (6) can be held in equilibrium depending on exhaust gastemperature. Note also, that equation (3) can occur but is notpreferred. The CO and H₂ generated according to equations (4) through(6) are then employed for regeneration, for example, as follows:$\begin{matrix}\left. {X\left( {NO}_{3} \right)}_{2}\rightarrow{{XO} + {2{NO}} + {\frac{3}{2}O_{2}}} \right. & (7) \\\left. {X\left( {NO}_{3} \right)}_{2}\rightarrow{{XO} + {2{NO}_{2}} + {\frac{1}{2}O_{2}}} \right. & (8) \\\left. {{NO} + H_{2}}\rightarrow{{H_{2}O} + {\frac{1}{2}N_{2}}} \right. & (9) \\\left. {{NO}_{2} + {2H_{2}}}\rightarrow{{\frac{1}{2}N_{2}} + {2H_{2}O}} \right. & (10) \\\left. {{NO} + {{CO}({Rh})}}\rightarrow{{\frac{1}{2}N_{2}} + {CO}_{2}} \right. & (11) \\\left. {{NO}_{2} + {2{CO}}}\rightarrow{{\frac{1}{2}N_{2}} + {2{CO}_{2}}} \right. & (12)\end{matrix}$where X is provided in a washcoat. A lambda less than or equal to 1,which denotes a low oxygen potential in the exhaust gas, favorsreactions (7) through (12); this is not the case, in general, whenlambda is above 1.

In general, a regeneration strategy can be employed targeting aregeneration flow and temperature of exhaust gas through the LNA.Catalyst 18 helps provides a hot and rich environment as is desirable toensure regeneration. A reductant provided to catalyst 18 duringregeneration is oxidized and reformed to provide an exhaust gasenvironment that has a low oxygen potential and includes effectivereductants (from the catalyst or from reductant store 44) forregeneration such as CO and hydrogen.

As noted above, however, the regeneration temperature for the exhaustgas may need to be hotter in general than the exhaust gas leaving block10 over some engine operating conditions—see area 802. Therefore, duringregeneration, it can be beneficial to retain heat generated in catalyst18 or block 10 in the exhaust gas delivered to LNA 16. Where it waspreferable to have LNA 16 well after or otherwise thermally “distant”from block 10 during an adsorption cycle, it can be desirable to reducethis thermal distance during regeneration. As such, referring to FIG. 2,reductant from catalyst 18 is directed to LNA 16 at appropriate exhaustgas temperatures to provide for the sought regeneration environment byway of line 12 a. As catalyst 18 has been lit off to reduce the exhaustgas environment, the resulting rise in exhaust temperature duringoxidation of the exhaust gas is sufficient generally for regeneration ofLNA 16. Therefore line 12 a in general should be sufficient toregenerate (NOx) LNA 16. If there is too much heat loss through line 12a, then hot line 49 could be employed. Note that the sensors (singularor plural) shown disposed in the aftertreatment system prior to catalyst18 and LNA 16 can be employed to control flow through LNA 16 duringregeneration. The sensors could also be disposed after catalyst 18 asrequired.

It is also possible to use an off-line reformer for directing areductant into the exhaust line just prior to LNA 16. This could makehot line 49 unnecessary. The reformer could heat the exhaust gas asneeded by providing a hot gas (such as air) with the reductant. Such asystem could also incorporate the benefits of bypass 20 by reducing theamount of exhaust gas to be heated and oxidized. Further, the coolingline can be employed to control temperature during an adsorption cycle.

Referring to FIG. 2, an optional close-coupled catalyst 32 can beprovided to increase exhaust gas temperatures when desired. Theproximity of catalyst 32 to engine block 10 helps ensure that exhaustgas is not too cool to oxidize the exhaust gas environment. Therefore,when the controller detects an exhaust gas temperature below a thresholdtemperature, valve 34 will provide reductant upstream of catalyst 32,heating and oxidizing the exhaust gas well upstream of LNA 16. This isuseful when the engine is operating at low loads. In low load operation,the exhaust gas exiting block 10 is relatively cool. Extra catalyst 32also helps to light off catalyst 18, when needed. Catalyst 18 can belocated at a position in the exhaust gas path which is a compromisebetween being proximate to LNA 16 and being proximate to block 10, whileLNA 16 and block 10 are thermally removed from each other.

Referring to FIG. 3, a turbine driven blower is employed to controltemperature of exhaust gas between catalyst 18 and LNA 16. Where exhaustgas is determined to be undesirably cool for regeneration, the load onturbine driven blower 82 is reduced or eliminated. Here, line 91 isprovided to direct intake air through valve 88 reducing or eliminatingthe load and therefore, maintaining some of the exhaust gas temperature.Alternatively, or in addition, hot line 86 can be employed to bypassturbine driven blower 82 when exhaust gas heat needs to be maintained.As would be apparent to a persons skilled in the technology involvedhere, the system shown in FIG. 3 could operate with only hot line 86.

Referring to FIG. 4, cooling loops 144, 146 and 148 can be employed toadjust exhaust gas heat where hot line 142 is available to divert heatedand oxidized exhaust gas around either turbine 152, heat exchanger 150or the extension of lead line 12 from loop 148. In addition,combinations of the systems discussed above, in parallel or in seriescan be employed.

As shown in FIG. 2, sensors can be placed in the aftertreatment systemto monitor temperature and, according to those readings, control flow ofexhaust gas during regeneration.

A regeneration cycle targeted at regeneration of LNA 16, will usuallyfail to de-sulfate LNA 16. Within LNA 16, X(SO_(x)) also uses upadsorbing sites that would otherwise be available to remove NOx.Therefore, in order to maintain the efficiency of LNA 16, in addition toa regeneration cycle, a de-sulfation cycle is also requiredperiodically.

During a de-sulfation cycle, an example set of reaction conditionsacross catalyst 18, where methane is the reductant, comprises:$\begin{matrix}\left. {{CH}_{4} + {2O_{2}}}\rightarrow{{CO}_{2} + {2H_{2}O}} \right. & (13) \\\left. {{CH}_{4} + {\frac{1}{2}O_{2}}}\rightarrow{{CO} + {2H_{2}}} \right. & (14)\end{matrix}$

The resulting rich and hot exhaust gas environment is employed forde-sulfation as follows:X(SOx)→SOx  (15)where X is in a washcoat.

As with regeneration, lambda should be low (quantitatively, a valuebelow one) to promote reaction 7.

In addition to providing a rich exhaust gas environment, the temperatureof the exhaust gas needs to be held at a temperature sufficient foreffective de-sulfation. The temperature required for de-sulfation ishigher than the temperature required for regeneration and typicallyhigher than the temperature of the exhaust gas from block 10. In theembodiment of FIG. 2, when a de-sulfation cycle is needed, hot line 49is opened to shorten the distance traveled by the exhaust gas bybypassing line 12 a of line 12. This helps to ensure that the heat fromthe exhaust gas is not dissipated significantly as the exhaust gas flowsfrom catalyst 18 to LNA 16. As well, referring to FIGS. 3 and 4, if, inaddition to long route, heat exchanger 150 or turbine driven blower 82or turbine 152 are employed, the hot line 49 can bypass these heatreducing systems as needed. The process is similar to that needed forregeneration. However, the temperatures sought for de-sulfation of LNA16 are much higher referring to area 806 of FIG. 1.

The adsorption, regeneration and de-sulfation cycles can be controlledthrough an open-loop control, based on selected parameters from theengine map, or closed-loop control, based, in part, on the exhaust gastemperature and the reactive capacity of catalyst 18 at the givenexhaust gas temperature. By way of example, one open-loop control uses acalibration of the treatment system over a range of engine operatingconditions to estimate the time required for LNA 16 to be regenerated orde-sulfated in light of the properties of catalyst 18. In suchembodiments, the controller monitors such variables as the engine loadand speed, and then determines from a look-up table, the time needed forregeneration or de-sulfation.

Open-loop control can be driven by such conditions as torque, speed,intake manifold temperature, intake manifold pressure, exhaust gastemperature and exhaust gas pressure prior to the catalysts as well asother conditions known to persons skilled in the technology involvedhere. The system can be calibrated such that the engine operatingconditions, which are indicative of NOx and sulfur content in theexhaust gas, are employed to estimate when regeneration or de-sulfationLNA is desirable.

The time required for de-sulfation is somewhat dependent on an assumedrange of sulfur content in the exhaust gases, which can vary dependingon such factors as the source of the fuel employed in the engine and thesource of the lubricating oils employed in the engine.

A closed-loop control can be employed to determine when to commence aregeneration or de-sulfation cycle and how to efficiently operate eachcycle in light of the aftertreatment architecture chosen. By way ofexample, referring to one or more of FIGS. 2 through 4, one such controlstrategy for selecting a de-sulfation cycle can monitor NOx levelswithin lead line 12 downstream of LNA 16 over the course of manyregeneration cycles. When the capacity of the LNA falls below apredetermined level, the controller can direct a de-sulfation cycle. Thecapacity of the LNA can be measured between regeneration cycles. Whenthe length of time between regeneration cycles falls below apredetermined level, then the controller will commence a de-sulfationcycle. The controller can control exhaust gas flow and the introductionof reductant to provide a de-sulfation strategy that helps to limit theuse of reductant. For regeneration cycle control, the NOx slip throughLNA 16 can be measured to select commencement of a regeneration cycle.

During an adsorption, regeneration or de-sulfation cycle, the exhaustgas is provided to the LNA as lean exhaust gas (during adsorption) or asa rich exhaust gas (oxygen depleted environment) and with a temperatureappropriate for the adsorption, regeneration or de-sulfation cycle, asthe case may be.

The flow of exhaust gas through the NOx LNA during regeneration isreferred to as the regeneration flow herein. The flow of exhaust gasthrough the LNA during de-sulfation is referred to as de-sulfation flowherein.

Referring to FIG. 2, during a regeneration cycle or a de-sulfationcycle, controller 64 determines a regeneration or de-sulfation strategybased, generally, on the exhaust gas flow, the exhaust gas temperature,a desired exhaust gas flow chosen considering the reactive capacity ofcatalyst 18 at a given exhaust gas temperature, and lambda of theexhaust gas from the engine. The regeneration and de-sulfation strategyfor a given regeneration cycle or de-sulfation cycle can be done by anopen-loop or closed-loop strategy as discussed above. The regenerationand de-sulfation strategy can be controlled by the quantity and rate ofthe reductant introduced into the exhaust gas from store 44, and by theamount of exhaust gas flow through hot line 49 dictated by valve 51.

Optionally, a bypass can also be provided prior to catalyst 18. Bypassline 20 with flow controlled by valves 24 and 30 can help to reduce theamount of exhaust gas that needs to be oxidized or heated during eitherregeneration or de-sulfation. The goal is to provide an exhaust gasenvironment wherein lambda is below or equal to one and the temperatureof the exhaust gas is high enough to promote either reaction (7) through(12) or (15) as the case may be. The reductants are oxidized to providethe energy required to heat the exhaust gas.

During regeneration, regeneration flow includes a portion of exhaust notdiverted through bypass 20 that is oxidized and heated and routed, inmany cases, through line 12 a.

De-sulfation flow is directed through hot line 49 so that it retainsmore heat compared to the case where the exhaust gas is routed throughline 12 a of line 12.

At commencement of a de-sulfation cycle, controller 64 causes valve 51to open and valve 57 to close. The de-sulfation flow bypasses line 12 ato some extent, depending on the control strategy chosen and the valveposition chosen for valve 57 in line 12 a. Bypass line 20 is helpful toensure efficient regeneration and de-sulfation; however, it is notmandatory. The system is capable of providing full exhaust flow throughthe LNA during de-sulfation.

Note that oxidation through the LNA with other reductants such ashydrogen, methane or other hydrocarbons can also provide an exothermrequired to provide de-sulfation temperatures across the LNA and thedesired rich exhaust gas environment.

Using the variables considered above for open loop control of theaftertreatment system, the controller is preferably calibrated to directflow of exhaust gas through the LNA and reductant into the exhaust gasbased on the engine speed and load just prior to and during eitherregeneration or de-sulfation cycles. Engine intake manifold temperature,intake air mass flow, fuel flow or intake manifold pressure can also beemployed as indicators of exhaust gas properties that are useful forcontrolling the de-sulfation cycle. A constant de-sulfation cycle timecan also be employed. This can be appropriate as the de-sulfation cycletime is relatively long as compared to such variables as the catalystlight off time and cycle variations related to varying exhaust gas flow.

An open-loop strategy employs an engine calibration that considers oneor more engine operating conditions, each of which is indicative of atleast one of exhaust gas temperature, flow and lambda value. Thecontroller is calibrated to direct a desired flow of exhaust gas throughthe LNA based on the characteristics of catalyst 18 and LNA 16. Alook-up table can be employed to determine whether the exhaust gas flowexceeds the desired regeneration or de-sulfation flow and, if so,controller 64 can cause excess exhaust gas to be diverted around LNA 16via bypass line 20. The desired bypass flow is achieved by adjustingvalves 24 and 30 to match the target de-sulfation flow though LNA 16.

The look-up table can also be employed to provide a desired flow rateacross hot line 49. As mentioned above, valve 51 can be opened at thecommencement of a de-sulfation or a regeneration cycle to direct asignificant portion of the regeneration or de-sulfation flow through hotline 49. Valve 57 disposed in line 12 a can provide additional controlover the flow through hot line 49 during regeneration or de-sulfation.

Valves suitable for the purpose described for valves 51 and 57 are wellknown. For example, each valve described in the embodiment of FIGS. 2through 4 could be a simple two position valve, a multi-position valve,or a variable position control valve, with the choice of valve typebeing dictated by cost and the desired degree of control. Also, one ofvalves 51 or 57 could be eliminated, reducing control, but simplifyingcontrols and reducing costs and maintenance by removing a movingcomponent. In each case, the controller can adjust de-sulfation flow bysplitting the flow through line 12 a and hot line 49.

With reference to the embodiment provided in the FIG. 2, valves 51 canalso be eliminated retaining an operable system. Regeneration andde-sulfation flow and adsorption exhaust gas flow control would need toconsider that a portion of the de-sulfation flow would be directed fromcatalyst 18 to LNA 16 through hot line 49 during the range of operatingmodes. By continuously splitting the exhaust flow in this manner, theexhaust gas temperature can be elevated at LNA 16. Another means couldbe provided, where desired, for managing temperature to keep the exhaustgas below a target temperature during an adsorption cycle.Alternatively, without valve 57, there will be a quantity of exhaust gasflow through line 12 a, and the controller would need to consider this.In each case, closed-loop strategies can be combined with the above. Insome closed-loop strategies, temperature sensor 58 can be employed tofeed data to controller 64 that can be employed by controller 64 tocontrol the efficiency of the regeneration and de-sulfation cycles.

The look-up table for an open-loop control can also provide a targetreductant concentration prior to catalyst 18 during regeneration orde-sulfation. The engine operating conditions provide information aboutthe exhaust gas temperature, flow and lambda of the exhaust gas fromblock 10. The temperature of the exhaust gas can be employed todetermine the amount of reductant required in order to meet the targettemperature range for the exhaust gas during regeneration andde-sulfation cycles. This target temperature range should be held belowa temperature that might damage the catalyst and above a temperaturesuitable for efficient reformation of reductant and, therefore,regeneration or de-sulfation of LNA 16. Moreover, the lambda of theexhaust gas, estimated from the engine operating conditions, determinesthe amount of reductant required to provide a sufficiently rich exhaustgas environment to support efficient regeneration or de-sulfation.

Referring again to FIG. 1, a closed-loop strategy could also be employedwherein the temperature could be measured prior to or after catalyst 18(see sensor 58 shown before catalyst 18 in the embodiment shown) andprior to LNA 16 through line 62. The load and speed of the engine couldbe employed by the controller to determine the exhaust gas flow based onlook-up tables. A flow meter within the exhaust line could also beemployed for further closed-loop control. The look-up table along withsensor information can be employed to determine the flow of reductant tobe introduced into lead line 12 and how much flow of exhaust gas, ifany, to direct through valve 24 and line 20 during regeneration orde-sulfation cycles to maintain a target regeneration or de-sulfationflow and regeneration or de-sulfation temperature.

When exhaust gas flow is too high for catalyst 18 to allow completeoxidation of methane or too high to de-sulfate efficiently, some flow isdirected into bypass line 20 until the desired flow is met.

If temperature prior to LNA 16 is too high or too low, the methanequantity can be adjusted to achieve the desired de-sulfationtemperature. This can also be done monitoring the temperature into orout of catalyst 18.

As with the open-loop system above, de-sulfation flow through hot line49 can be determined by a calibration provided to the controller thatwould include an engine map corresponding to a flow split through hotline 49 and line 12 a. This is dependent on the control available to thecontroller resulting from the availability and type of valves in line 12a and/or hot line 49. Also, an open-loop control could be employed thatwould also consider the temperature of the regeneration or de-sulfationflow prior to LNA 16 and direct that de-sulfation flow through hot line49 and line 12 a to target the desired temperature required to ensureefficient regeneration or de-sulfation of LNA 16. The temperature canalso be employed to control valve 36 to vary reductant flow or quantityproviding a hotter exhaust gas into LNA 16.

As noted above, a closed-loop strategy may be preferred depending oncost and application considerations. The open-loop strategy discussedabove utilizes a calibration of the system that provides a targetreductant injection rate and quantity over a regeneration andde-sulfation cycle that is based on the engine operating parameters suchas load and speed, and could eliminate dynamic monitoring and the addedcomplexity in hardware and software for the system. However, thetrade-off is that such a strategy is more likely to regenerate orde-sulfate LNA 16 incompletely or less efficiently.

Controls, as described above, can also be employed to controlembodiments having a turbine-driven blower 82. Here, however, control isneeded to monitor the flow of air into lead line 12 through valve 80during adsorption cycles. During a regeneration or de-sulfation cycle,valve 90 can be opened to direct all or a portion of the flow aroundturbine driven blower 82, as desired to match the temperaturerequirement for exhaust gas through LNA 16. Although, not shown in thisembodiment, as would be understood by persons skilled in the technologyinvolved here, a bypass could also be employed between catalyst 18 andLNA 16 (upstream of catalyst 18 and downstream of LNA 16). This bypasswould be employed in the same manner as described for the firstembodiment in FIG. 1.

In addition to hot line 86, line 91 could also be employed to removeload from turbine driven blower 82 when there is a need to maintainexhaust gas heat.

For the embodiment shown in FIG. 3 flow sensors through valve 80 andtemperature sensors within the line 12 could be employed to provideclosed-loop control for adsorption, regeneration and de-sulfationcycles.

More generally, referring to FIG. 4, the three heat exchangers orturbines could also be controlled as needed to manipulate exhausttemperature through to LNA 16. Open or closed-loop controls couldcontrol flow and temperature through the exhaust line into LNA 16 toensure the exhaust gas temperature falls within a desired rangeregardless of the operating demands on the engine and whetheradsorption, regeneration or de-sulfation is sought from theaftertreatment system.

To simplify the system, an alternative to using variable flow controlvalves is to use two position valves (or for that matter other multipleposition valves). For example, for valves 24, 30, 51 and 57 thecontroller can elect from one of a plurality of possible settings tocontrol flow through lines 12, 20 and 49. Valve 30 can be fully open orpartially open. Valves 24, 51 and 57 can be closed or open. Therefore,controller 70 can select a position for each valve according to theengine operating parameters in order to match exhaust flow through line12 to a pre-determined target value. That is, at low speed and load,valve 30 and 51 are open fully, and valves 24 and 57 are closed. Athigher loads and speeds, valves 24, 30 and 51 are fully opened and valve57 can be closed. At still higher speeds and loads, valve 30 ispartially open and valves 24 and 51 are opened while valve 57 can beopened or closed.

As would be understood by persons skilled in the technology involvedhere, valves employed in the aftertreatment systems shown could be anysuitable flow control mechanism and need not be limited to valves.

Other valve configurations can be employed as well. More flexibility forthe controller to manage flow during adsorption, regeneration andde-sulfation cycles helps the controller to meet a target pre-determinedflow for each cycle. A trade-off is that such flexibility can result ina system that requires more expensive valves and more complicatedsoftware to control those valves.

FIG. 5 shows an additional embodiment of the present technique. Here, asecond LNA is added: SOx adsorber 100. Exhaust lines include lead line12, bypass line 20, line 12 a, hot line 49 and sulfur line 106. Tocontrol flow through SOx adsorber 100, valves 102 and 104 are employedto control exhaust gas flow through LNA 16 or around LNA 16 by way ofsulfur line 106. Valves 108 and 110 are employed to control bypass flow(where desired) around LNA 16, catalyst 18 and SOx adsorber 100. Notehere, as mentioned above, as a demonstration of an alternative flowcontrol architecture, the bypass control valves 108 and 110 are both inbypass line 20 where one of these valves was in lead line 12 in theembodiment demonstrated in FIG. 2 above.

The embodiment shown in FIG. 5 is a version of the embodiment shown inFIG. 2 which has been modified to include SOx adsorber 100. SOx adsorber100 extends the time between de-sulfation cycles. LNA 16 still needsperiodic de-sulfation. However, SOx adsorber 100 in line 12 a removesmost of the Sox. The concentration of sulfur compounds in exhaust gaspassing through LNA 16 during an adsorption cycle is small. Thestructure shown however, still needs to allow for de-sulfation of bothLNA 16 and the SOx LNA 100.

LNA 16 can be de-sulfated substantially as described above. The heatrequired to effect de-sulfation is provided by catalyst 18, reductantfrom reductant store 44 (introduced through line 42 and valve 36) andhot line 49 ensuring heat in the exhaust is maintained for de-sulfationof the LNA.

A SOx adsorber regeneration cycle (like LNA regeneration cycles,designed to release the primary trapped component—sulfur compounds inthis case—periodically to free up the adsorber for further adsorption),needs to also be incorporated. When SOx adsorber 100 is “full”, exhaustgas is oxidized with reaction of reductant from store 44 across catalyst18. The resulting rich exhaust gas environment through SOx adsorber 100releases sulfur into the exhaust gas flowing from SOx adsorber 100. Thisis designed to happen when exhaust gas temperatures are within a rangesimilar for release of NOx from LNA 16. This can allow regeneration ofNOx and SOx adsorbers at the same time as long as released sulfur isdirected around LNA 16. Here a line directly from catalyst 18 to LNA 16would be needed to provide relatively sulfur-free exhaust gas requiredfor regeneration of LNA 16. Some of that same exhaust gas would bedirected to SOx adsorber 100 and the resulting sulfur-rich exhaust gaswould be passed out of the aftertreatment system via line 106. That is,the resulting exhaust gas is routed through valve 104 and from thesystem along line 106. In the embodiment shown, it is important thatvalve 102 be closed to avoid release of sulfur rich exhaust gas throughLNA 16 during a SOx adsorber regeneration cycle.

The regeneration of NOx and SOx adsorbers could occur in series wherethe exhaust gas is heated as required for regeneration of SOx adsorberand bypassed through sulfur line 106 immediately after which the exhaustgas is passed through LNA 16 once the regeneration of the SOx adsorberis complete and little sulfur is directed to LNA 16 for a regenerationcycle of this catalyst.

Bypass line 20 can also be employed to help with efficiency during SOxadsorber regeneration cycles by directing some exhaust gas throughbypass line 20 thereby reducing the energy required to heat theremaining exhaust gas through line 12 a.

A clean-up catalyst, not shown, can optionally be provided to ensurethat hydrogen sulfide released during SOx adsorber regeneration orduring de-sulfation is converted to a sulfate.

Note, in this embodiment, that it is less important to include hot line49, employed to de-sulfate LNA 16. As the periods between de-sulfationcycles of LNA 16 are increased considerably with the introduction of theSOx adsorber 100, the loss in efficiency of additional heating for theexhaust gas for de-sulfation to make up for greater heat loss by routingthe exhaust gas through line 12 a is less important.

In general, an appropriately sized SOx adsorber, could, by way ofexample, increase the time between de-sulfation cycles of LNA 16 by afactor of 50. By way of example, the SOx adsorber, depending on the fuelemployed, could be sized one-quarter of the size relative to the LNA. Asnoted above, the SOx adsorber could be selected to allow for a SOxadsorber regeneration temperature range similar to the NOx adsorberregeneration temperature thus reducing complication in the system byallowing for similar conditions for two different processes. Also, whereexhaust flow can be reversed or separated to flow through SOx adsorberand NOx adsorber separately from the same catalyst, by way of example,then regeneration of both of these adsorbers can occur at the same time.

Sulfur line 106 is not essential to the system, however, without it,regeneration of SOx adsorber should either be avoided or should employ areverse flow strategy like the one taught for the embodiment discussedbelow (see FIG. 6 and the accompanying discussion).

FIG. 6 shows a further embodiment of the present technique that includesbypass line 20 with valves 108, 110 and, in the exhaust line, catalyst18, SOx adsorber 100 and LNA 16. This embodiment also includes lead line12 that branches into reverse flow line 208. Exhaust gas flow throughline 208 is controlled by valves 200 and 204. In general, exhaust linesinclude lead line 12, bypass line 20, line 208 and reverse flow exit202.

Valve 201 controls flow out of reverse flow exit 202. Valve 206 controlsflow out of lead line 12. Reductant store 44 is provided with reductantline 42. Valve 36 controls flow of the reductant to the catalyst whenregeneration and de-sulfation are required.

In operation, during an adsorption cycle, exhaust gas flows from engineblock 10 through line 12 and SOx adsorber 100, LNA 16 and out throughvalve 206. Valves 108, 201 and 204 are closed forcing exhaust gas toflow through valve 206 and out of the aftertreatment system. Control ofthe system can be as described above.

When a regeneration cycle is required, flow is maintained throughcatalyst 18 where valve 36 is opened to introduce reductant. The rich,heated exhaust gas can be directed into LNA 16 through valve 204 and outof the system through line 202. As discussed above, some exhaust gas canbe directly bypassed around catalyst 18 via line 20.

When the system controller chooses to de-sulfate LNA 16, valves 36 and204 are opened. Valves 108 and 110 can be opened if bypass of someexhaust gas is preferred. During de-sulfation of LNA 16, exhaust gasflows from catalyst 18, where with the introduction of a reductant tocatalyst 18, the exhaust gas is oxidized, heated and bypassed throughvalve 204 and line 208 to LNA 16. Valve 206 is closed, routing theexhaust gas through LNA 16. Eventually, the exhaust gas with sulfur fromLNA 16 is directed from lead line 12 to line 202 and through valve 200out of the aftertreatment system.

Similarly, exhaust gas is routed in the same direction duringregeneration of SOx adsorber 100. Heated exhaust gas is directed to SOxadsorber 100 by way of line 208 through valve 204 and LNA 16. Afterreleasing sulfur in SOx adsorber 100, the exhaust gas is expelled fromthe system by way of line 202 through valve 200.

This embodiment could operate with a closed-loop system. A sensor couldbe placed within the aftertreatment architecture to monitor sulfur slipor NOx slip from SOx adsorber 100 or LNA 16 for determining when theseadsorbers need to be regenerated or de-sulfated, after which the valveswould be appropriately controlled. The sensor could also measure flowrates through parts of the aftertreatment system to help target the flowrequirements through parts of the system during adsorption, de-sulfationand regeneration cycles. As well, the system could be calibrated to takeadvantage of an open-loop control strategy that determines or estimatesthe flow rate of exhaust gas and engine operating conditions toapproximate when regeneration cycles should occur and when de-sulfationcycles should occur.

During regeneration and de-sulfation cycles where bypass line 20 isemployed, the NOx levels out of line 12 can increase substantially, asthe engine is continuing to operate without NOx treatment of the exhaustgas routed through bypass line 20. Once regeneration and de-sulfationare complete, however, NOx quickly falls as exhaust gas is routedthrough recently regenerated and de-sulfated LNA 16. Therefore, as wellas a desire to reduce fuel consumption (consumption of methane), shortregeneration and de-sulfation cycles also limit the amount of NOxemitted during de-sulfation through bypass line 20. The longer theperiod of time needed for regeneration and de-sulfation cycles, the morecumulative exhaust gas flows through bypass line 20.

Catalyst 18 is generically described as a bed that promotes the relevantreactions noted above to provide a desired exhaust gas with a lambdabelow or equal to one and at or above the regeneration or de-sulfationtemperature, as the case may be. As this catalyst needs to heat exhaustgas quickly to a very high temperature, it also needs to be selectedfrom materials able to withstand the temperature needed for the exhaustgas and be capable of heating exhaust gas to those temperatures quickly.A metal substrate for carrying the catalyst is generally preferred,rather than, for example, a ceramic substrate, if the metal substrateimproves thermal response to catalyst 18. As noted above, the quickerthe thermal response, the faster the regeneration or de-sulfation cyclecan be completed, thereby reducing the amount of untreated exhaust gasallowed to flow through bypass line 20 where employed.

Catalyst 18 can be a partial oxidation catalyst that partially oxidizesa reductant (such as methane) and reforms that reductant—see reactions(4) through (6) for the methane example.

Catalyst 18 can also be a back-to-back oxidation catalyst and reformersharing a common boundary surface. Such catalysts first oxidizereductant until the oxygen potential is reduced sufficiently. These twocatalysts, the oxidation catalyst and reformer, can also be disposed inline 12 in series and need not share a common boundary surface. Also, acombination reformer and oxidation catalyst that integrates the reformerand oxidation catalyst together in a mixed catalyst could be employed.Each option provides trade-offs between cost and efficiency.

An oxidation catalyst can be a component of catalyst 18, and can be anoxidization catalyst suitable for oxidizing the exhaust gas to reducethe oxygen content. By way of example, a suitable oxidation catalyst canpromote the following reactions: $\begin{matrix}\left. {{C_{x}H_{y}} + {\left( {x + \frac{y}{4}} \right)\quad{O_{2}({Pt})}}}\rightarrow{{x{CO}}_{2} + {\frac{y}{2}H_{2}O}} \right. \\\left. {{C_{x}H_{y}} + {\left( {x + \frac{y}{4}} \right)\quad{O_{2}({Pd})}}}\rightarrow{{x{CO}}_{2} + {\frac{y}{2}H_{2}O}} \right. \\\left. {{C_{x}H_{y}} + {\frac{x}{2}{O_{2}({Pd})}}}\rightarrow{{x{CO}} + {\frac{y}{2}H_{2}}} \right. \\\left. {{CO} + {\frac{1}{2}O_{2}}}\rightarrow{CO}_{2} \right.\end{matrix}$By way of example only, for the operating conditions known for thisapplication, a suitable washcoat formulation comprises Al₂O₃. Othersuitable washcoat formulations can also be employed, as would beunderstood by persons skilled in the technology involved here.

A reformer can be a component of catalyst 18. Reformers suitable forthis application are well known. The reformer is preferably suitable toconvert a hydrocarbon with water to CO and H₂. By way of example, thereformer can be a precious metal-based catalyst with washcoat materialsincluding Al₂O₃.

FIG. 2 shows an additional catalyst, close-coupled catalyst 32,positioned near engine block 10. Some systems can include such acatalyst disposed close to the engine to ensure that the exhaust gas ishot enough to support oxidation of reductant. That is, there are someaftertreatment system designs that would benefit from employing aclose-coupled catalyst near the engine block so that the exhaust gastemperature under low load and/or speed or idle conditions can beprevented from falling below a threshold limit at which stable oxidationof methane in catalyst 18 would be compromised. The close-coupledcatalyst is typically physically smaller than catalyst 18 and thereforemore easily accommodated near the engine. It would not replace catalyst18. A larger catalyst allows the system to take advantage of higherexhaust gas flows to provide quick de-sulfation cycles. Therefore, undersuch conditions, there are advantages in having close-coupled catalyst32 near engine block 10 with line 40 feeding methane into the exhaustgas prior to such catalyst. Catalyst 32 oxidizes the reductant providedfrom store 44 to heat the exhaust gas to a temperature suitable to allowcatalyst 18 to light off satisfactorily.

Note also that the close-coupled catalyst could be placed prior to aturbine, and the heated exhaust gas, partly heated in the turbine, couldbe employed to help drive the turbine for greater flexibility for theengine.

As noted above, the adsorption, regeneration, and de-sulfation cyclesare dependent on the exhaust gas temperature. For example, forregeneration and de-sulfation it is important that the exhaust gasintroduced into catalyst 18 has a temperature above a minimumtemperature to ensure that the catalyst is “lit-off” initially. Onestrategy for ensuring an appropriate exhaust gas temperature from thecombustion chamber is to choose a combustion strategy or combustiontiming that ensures either relatively late heat release, as might be thecase with spark ignited engines, for regeneration or de-sulfationcycles, or by ensuring quick heat release at higher loads foradsorption. Also, a delayed or second direct injection of fuel into thecombustion chamber late in the power stroke when regeneration orde-sulfation is required will help heat the exhaust gas from engineblock 10. This can also reduce NOx levels with associated benefitsduring regeneration or de-sulfation cycles as a quantity of exhaust gascould be directed through the bypass line without NOx treatment. Areduced NOx level has benefits here. Other strategies are well known topersons skilled in the technology involved here.

As hydrocarbons or hydrogen can be effective reductants, store 44 can bethe fuel storage tanks if the engine is fueled by the reductant. Forexample, for natural gas engines, natural gas can be employed as thereductant.

Also, valves 34 and 36 can be injectors that directly inject a suitablereductant, such as methane, into lead line 12. Injectors would providegreater control over the timing and quantity of methane and, therefore,greater control over the duration of the regeneration or de-sulfationcycles.

LNA 16 typically adsorbs and stores NOx in the catalyst washcoat whileoperating under lean conditions and NO₂ can be released and reduced toN₂ under rich operating conditions when a de-sulfation mixture, thatincludes hydrogen and rich exhaust gas, is passed through the LNA. Asnoted above, the following shows typical operation of the LNA under leanconditions: $\begin{matrix}\left. {{NO} + {\frac{1}{2}{O_{2}({Pt})}}}\rightarrow{NO}_{2} \right. \\\left. {{XO} + {2{NO}_{2}} + {\frac{1}{2}O_{2}}}\rightarrow{X\left( {NO}_{3} \right)}_{2} \right.\end{matrix}$and under rich conditions: $\begin{matrix}\left. {X\left( {NO}_{3} \right)}_{2}\rightarrow{{XO} + {2{NO}} + {\frac{3}{2}O_{2}}} \right. \\\left. {X\left( {NO}_{3} \right)}_{2}\rightarrow{{XO} + {2{NO}_{2}} + {\frac{1}{2}O_{2}}} \right. \\\left. {{NO} + {{CO}({Rh})}}\rightarrow{{\frac{1}{2}N_{2}} + {CO}_{2}} \right. \\\left. {{2{NO}_{2}} + {4H_{2}}}\rightarrow{N_{2} + {4H_{2}O}} \right.\end{matrix}$where X is provided in the washcoat and is typically an alkali (forexample, K, Na, Li, Ce), an alkaline earth (for example, Ba, Ca, Sr, Mg)or a rare earth (for example, La, Yt).

A further advantage can be realized if a fuel that combines a reductantsuch as methane and hydrogen as two major components of the fuel isemployed. By way of example, natural gas with 10% to 50% hydrogen mightbe appropriate as an engine fuel and appropriate for regeneration orde-sulfation cycles. Such a fuel could then be utilized in theembodiments discussed wherein the hydrogen introduced with the fuelprior to the oxidation catalyst could help to light off those catalystsand help to provide an exhaust gas environment with a lambda less thanor equal to 1. Further, by providing a quantity of hydrogen into theexhaust stream, the burden on catalyst 18 is reduced. Less reforming isrequired for de-sulfation due to the presence of hydrogen in theinjected fuel.

Reductants that could be employed include such things as diesel fuel,gasoline or other hydrocarbons as well as natural gas, methane, ethane,propane, butane or hydrogen or combinations of these fuels.

Whenever flow is referred to in this disclosure, it is the mass or molarflow rate of the gas in question.

Exhaust gas recirculation (EGR) can also be utilized to help reduce NOxemissions during regeneration or de-sulfation cycles when a bypass lineis opened. Increased EGR rates during regeneration or de-sulfation canreduce NOx generated in the combustion chamber, resulting in less NOxflowing through bypass line 20 and into the atmosphere. Further,increases in EGR can also be employed to reduce the concentration ofoxygen in the exhaust gas during regeneration or de-sulfation, reducing,in turn, the burden on the oxidation catalyst to reduce oxygen during aregeneration or de-sulfation cycle as well as reduce the amount ofreductant needed to burn off oxygen.

While particular elements, embodiments and applications of the presentinvention have been shown and described, it will be understood, ofcourse, that the invention is not limited thereto since modificationscan be made by those skilled in the art without departing from the scopeof the present disclosure, particularly in light of the foregoingteachings.

1. An aftertreatment system for treating NOx found in exhaust gasproduced during combustion of a fuel within a combustion chamber of anoperating internal combustion engine, said aftertreatment systemcomprising: an exhaust line for directing said exhaust gas from saidengine and through said aftertreatment system, said exhaust linecomprising a cooling line and a hot line for managing exhaust gastemperature during an adsorption cycle and a regeneration cycle; a leanNOx adsorber disposed in said exhaust line; a catalyst capable ofoxidizing a reductant and directing said oxidized reductant into saidexhaust gas; a reductant line for delivering a reductant from areductant store to said catalyst; a reductant flow control disposed insaid reductant line for controlling flow of said reductant into saidexhaust line; and a flow control for controlling flow of exhaust gasthrough said hot line and cooling line, wherein said exhaust line iscapable of delivering exhaust gas from said catalyst to said lean NOxadsorber.
 2. The aftertreatment system of claim 1 wherein said catalystis disposed in said exhaust line.
 3. The aftertreatment system of claim2 wherein said cooling line and said hot line are between said catalystand said NOx adsorber.
 4. The aftertreatment system of claim 2 whereinsaid cooling line is longer than said hot line.
 5. The aftertreatmentsystem of claim 2 further comprising a turbine disposed in said coolingline.
 6. The aftertreatment system of claim 5 wherein said turbinedrives an air blower disposed in an air dilution line and connected tocompress air and direct the compressed air into said cooling line. 7.The aftertreatment system of claim 2 further comprising an air blowerdisposed in an air dilution line for compressing and directing air intosaid cooling line.
 8. The aftertreatment system of claim 2 furthercomprising a heat exchanger disposed in said cooling line.
 9. Theaftertreatment system of claim 2 further comprising a close-coupledcatalyst in said exhaust line upstream of said catalyst, said reductantline capable of delivering reductant to said exhaust line upstream ofsaid close-coupled catalyst.
 10. The aftertreatment system of claim 2wherein said reductant line delivers said reductant to said exhaust lineupstream of said catalyst.
 11. The aftertreatment system of claim 2wherein said exhaust line comprises a by-pass line capable of directingsaid exhaust gas around said catalyst.
 12. The aftertreatment system ofclaim 2 further comprising a SOx adsorber disposed in said exhaust lineto remove SOx from said exhaust gas before said exhaust gas passesthrough said NOx adsorber during The adsorption cycle.
 13. Theaftertreatment system of claim 12 wherein said exhaust line furthercomprises a sulfur line for bypassing said exhaust gas around said NOxadsorber when regenerating said SOx adsorber and a flow control forcontrolling flow of exhaust gas through said sulfur line.
 14. Theaftertreatment system of claim 12 wherein said hot line is a reverseflow line capable of alternating flow of said exhaust gas where said NOxadsorber is upstream of said SOx adsorber.
 15. The aftertreatment systemof claim 2 wherein a cooling line length is chosen relative to a hotline length such that more exhaust gas heat is dissipated through saidcooling line than would occur through said hot line.
 16. Theaftertreatment system of claim 2 wherein a cooling line material ischosen such that more exhaust gas heat is dissipated through saidcooling line than would occur through said hot line.
 17. A method ofoperating an aftertreatment system for removing NOx from exhaust gasgenerated by combustion of a fuel in at least one combustion chamber ofan internal combustion engine, said method comprising an adsorptioncycle, a regeneration cycle and a de-sulfation cycle: during saidadsorption cycle: cooling said exhaust gas to within a predeterminedadsorption temperature range when said exhaust gas is above saidadsorption temperature range, directing said cooled exhaust gas throughan exhaust line to a lean NOx adsorber disposed in said exhaust line,during said regeneration cycle: directing a first portion of saidexhaust gas through a bypass line around said lean NOx adsorber;oxidizing at least a second portion of said exhaust gas to a lambdavalue of less than or equal to 1, heating said at least said secondportion of said exhaust gas to within a predetermined regenerationtemperature range when said at least said second portion of said exhaustgas is below said regeneration temperature range; directing saidoxidized and heated exhaust gas through said lean NOx adsorber, duringsaid de-sulfation cycle: oxidizing said exhaust gas to a lambda value ofless than or equal to 1, heating said exhaust gas to within apredetermined de-sulfation temperature range when said exhaust gas isbelow said de-sulfation temperature range directing said oxidized andheated exhaust gas through said lean NOx adsorber.
 18. The method ofclaim 17 wherein, during said adsorption cycle, said exhaust gas iscooled by introducing air into said exhaust gas.
 19. The method of claim17 wherein, during said adsorption cycle, said exhaust gas is cooled bydirecting said exhaust gas through a turbine.
 20. The method of claim 19wherein said turbine is employed to drive a blower for directing airinto said exhaust line upstream of said NOx adsorber.
 21. The method ofclaim 17 wherein, during said adsorption cycle, said exhaust gas iscooled by expanding said exhaust gas.
 22. The method of claim 17wherein, during said adsorption cycle, said exhaust gas is cooled bydirecting said exhaust gas through a heat exchanger.
 23. The method ofclaim 17 wherein, during said adsorption cycle, said exhaust gas iscooled by routing said exhaust line through a cooling line.
 24. Themethod of claim 17 wherein said at least said second portion of saidexhaust gas does not include said first portion of said exhaust gas. 25.The method of claim 17 wherein, during said de-sulfation cycle, aportion of said exhaust gas is directed through a bypass line aroundsaid lean NOx adsorber.
 26. The method of claim 17 wherein, during saidadsorption cycle, said exhaust gas is directed through a SOx adsorberdisposed in said exhaust line prior to directing said exhaust gasthrough said NOx adsorber.
 27. The method of claim 17 wherein saidexhaust gas is heated and oxidized by passing said exhaust gas through acatalyst with a reductant introduced into said exhaust gas.
 28. Themethod of claim 17 wherein said reductant is selected from the groupconsisting of hydrocarbons, hydrogen, and combinations thereof.
 29. Themethod of claim 28 wherein said reductant includes a hydrocarbonselected from the group consisting of natural gas, diesel, methane,ethane, butane, propane, and combinations thereof.